1. Field of the Invention
The present invention relates to a semiconductor device, a method of manufacturing the same, and a solid-state image sensor.
2. Description of the Related Art
As a solid-state image sensor such as a CCD or CMOS sensor, a back-side illumination solid-state image sensor capable of achieving higher sensitivity has been proposed. The back-side illumination solid-state image sensor has a photoelectric conversion element such as a photodiode on the front-side surface of a semiconductor substrate such as silicon, and uses the photoelectric conversion element to detect light incident on the back-side surface of the semiconductor substrate. However, if the semiconductor substrate is too thick, the incident light is absorbed in the substrate en route to the photoelectric conversion element, so a sufficient amount of light cannot reach the photoelectric conversion element. Hence, it is necessary to reduce the thickness of a semiconductor substrate having a photoelectric conversion element formed on its front-side surface, by thinning the semiconductor substrate from its back-side surface, to a target thickness. Japanese Patent Laid-Open No. 2001-257337 proposes a method of manufacturing such a solid-state image sensor.
Japanese Patent Laid-Open No. 2001-257337 describes a method of forming an image sensing element in an epitaxial layer formed on a porous silicon layer, and then separating a semiconductor substrate from the image sensing element using the porous silicon layer. However, the porous silicon layer is vulnerable, so especially when a relatively large semiconductor substrate is used, the semiconductor substrate may be separated upon collapse of the porous silicon layer while an image sensing element is formed in the epitaxial layer.